Carriers vying to sign you up for a new iPhone 8 or 8 Plus starting Friday face a tough problem: They can’t list the phone for below Apple’s prices, while in most cases Apple matches their installment-payment pricing but gives you an iPhone that isn’t locked for use on a single carrier.

They can, however, rip a page out of the used-car sales manual and push a deal on a related product: a trade-in offer on your current phone or a discount on a related gadget.

AT&T

• At AT&T, buying one of Apple’s new iPhones gets you a 32 GB LTE-equipped iPad for $99, not the $459 Apple charges. But you must sign up for two years of multiple-device service. Don’t think of this as a cheap way to get an iPad you’ll mostly use on Wi-Fi.

Even on AT&T’s cheaper Mobile Share Advantage plans, adding an iPad without extra data costs $10 extra a month. In that case, you’ll spend less over two years if you buy the $329 Wi-Fi-only model and use it with your phone’s mobile-hotspot feature.

But if the iPad will drain more than 10 GB of data a month — the hotspot limit on AT&T’s unlimited plans— you need an LTE model anyway. So take AT&T’s offer and budget for the $20 monthly surcharge to add that iPad to your plan.

Sprint

• Sprint, meanwhile, offers 50% off its lease rate for people who switch to Sprint by trading in an iPhone 7 or 7 Plus by Sept. 28. That slashes your two-year cost on an iPhone 8 to $350 from the usual $700 and lets you swap it for next year’s model in 12 months.

The savings do outstrip what you’d likely get for selling a year-old device: The gadget-resale site Gazelle.com says it will pay $285 for an unlocked good-condition iPhone 7, $245 if it’s locked to Sprint. But do you actually need to dump that phone? The 8 and 8 Plus don’t represent a huge advance over the 7 and 7 Plus.

Sprint also promises to beat any “nationally advertised lower price” for the new iPhones. It almost certainly won’t have to make good on that, since Apple controls iPhone pricing so tightly.

T-Mobile

• At T-Mobile, trading in a paid-off iPhone 6 or newer will get you $300 off the price of an iPhone 8 or 8 Plus, to be paid back in credits on your bill over 24 months. This deal works best if you have pre-7 iPhone--a device that’s lost a big chunk of its resale value (for instance, Gazelle only offers $115 for an entry-level unlocked 6) and is due for an upgrade.

Other phones only get T-Mo’s less-generous regular trade-in offers.

Verizon

• Verizon offers $300 back, paid over 24 credits on your bill, if you sign up for its unlimited plan and turn in an iPhone 6s or newer or any of the following Android phones: Samsung’s Galaxy S7, S7 Edge, S8 and S8+; LG’s G6; Google’s Pixel XL; and Moto’s Z2 Force.

Among those, the S7—$140 at Gazelle—offers the maximum return. Verizon also has a $200 trade-in deal for older models including the iPhone 6 and Galaxy S6, plus a $100 option for devices going back to the iPhone 5 and the Galaxy Note 4.

But if you use 5 GB or less data in a month, Verizon’s $55/month single-line plan — shown at its site if you pick out one phone and select a plan — will save $20 monthly compared to its $75 “Go Unlimited” plan. (These prices reflect a $5 discount for automatic payments.) And not only will the $480 saved outstrip the trade-in offer, you’ll also get the full-speed mobile-hotspot use that Verizon reserves for its $85 “Beyond Unlimited” plan.

If your existing phone doesn’t fit into the focus of any of these trade-in deals, don’t forget that you have another money-saving option: holding off for a few weeks. Apple’s not going to run out of the iPhone 8 or 8 Plus (the $999-and-up iPhone X, not due until October, may be another matter), so there’s no real cost to waiting.

(Disclosure: I also write for Yahoo Finance, a subsidiary of Verizon’s media division Oath.)

Rob Pegoraro is a tech writer based out of Washington, D.C. To submit a tech question, email Rob at rob@robpegoraro.com. Follow him on Twitter at twitter.com/robpegoraro.